A rectangular-parallelepiped of light in a volume shader
Thanks to Chebhou's setups (see question for links) I found something that fits my question. here is the node setup:  

But I wanted to know how to make the light inside from all sides...
here is the node setup


The important things to note are the placement of the object's origin (all rotations applied) and the value node controling the space between volume scatter and light, normalized. 0.2 means 20% up/down (Z), 20% left/right (Y) and 20% front/back (X). The last multiply node just adds strength to the light.